The HAB discrimination technique has obtained accurate results on MODIS and
MERIS data, correctly identifying 89% of Phaeocystis globosa HABs in the southern North Sea and 88% of
Karenia mikimotoi blooms in the Western English Channel. A linear transformation of the ocean colour
discriminants is used to estimate harmful cell counts, demonstrating greater accuracy than if based on
chlorophyll-a; this will facilitate its integration into a HAB early warning system operating in the
southern North Sea.